Diffraction gratings are utilized in a variety of technologies and can form an integral part of optical or spectral analysis tools in sensing, chemical analysis, and security applications. For example, diffraction gratings can be used as dispersive elements for spectrum analyzers or to select, tune, and expand the light spectrum of laser devices. Diffraction gratings can also be used as optical coupling elements in light and optical communication devices.
Diffraction gratings are typically manufactured by one of two conventional methods. The first method utilizes ruling engines, such as a precision stage equipped with diamond tips to produce mechanically ruled gratings. The properties of a mechanically ruled grating can thus vary based on the specific ruling engine used in its manufacture. In addition, gratings produced by a ruling engine can suffer from, for example, the presence of stray lines that can limit or adversely affect use in high impact spectrometers. A diamond turning process can be very slow, as the ruling diamond may need to travel a long distance to produce a single grating. For example, a square grating (10cm×10 cm) with a groove density of 1,000 grove/mm can require miles of diamond tip travel and take weeks to produce. Thus, the use of a ruling engine to manufacture a diffraction grating can be costly, requiring significant time and strict control of the production environment.
The second method for manufacturing diffraction gratings utilizes laser interference lithography to produce holographic gratings having sinusoidal grooves. In the manufacture of holographic gratings, lasers are used to etch a film coated on a substrate. The resulting etched substrate can have a regular pattern of grooves, which can be bombarded with an ion beam to produce a blazed grating and to enhance the efficiency of the resulting grating. While the laser interference lithography process can be faster than diamond turning techniques, the process can be limited by the laser beam size, which is typically on the order of millimeters. Thus, large gratings can still require significant manufacturing times. The laser interference lithography process be limited with respect to groove frequency. For example, gratings with groove densities less than a few hundred grooves per millimeter can require cumbersome and expensive optical recording systems.
Other recently developed techniques include imprint lithography techniques, where electron beam lithography and photolithography or embossing techniques are used to reproduce fine patterns from a mask onto a substrate. Thus, there is a need for improved manufacturing techniques for diffraction gratings. This and other needs are satisfied by the compositions and methods of the present invention.